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jdmainct.c (20366B)
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1 /*
2 * jdmainct.c
3 *
4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
7 *
8 * This file contains the main buffer controller for decompression.
9 * The main buffer lies between the JPEG decompressor proper and the
10 * post-processor; it holds downsampled data in the JPEG colorspace.
11 *
12 * Note that this code is bypassed in raw-data mode, since the application
13 * supplies the equivalent of the main buffer in that case.
14 */
15
16 #define JPEG_INTERNALS
17 #include "jinclude.h"
18 #include "jpeglib.h"
19
20
21 /*
22 * In the current system design, the main buffer need never be a full-image
23 * buffer; any full-height buffers will be found inside the coefficient or
24 * postprocessing controllers. Nonetheless, the main controller is not
25 * trivial. Its responsibility is to provide context rows for upsampling/
26 * rescaling, and doing this in an efficient fashion is a bit tricky.
27 *
28 * Postprocessor input data is counted in "row groups". A row group
29 * is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
30 * sample rows of each component. (We require DCT_scaled_size values to be
31 * chosen such that these numbers are integers. In practice DCT_scaled_size
32 * values will likely be powers of two, so we actually have the stronger
33 * condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
34 * Upsampling will typically produce max_v_samp_factor pixel rows from each
35 * row group (times any additional scale factor that the upsampler is
36 * applying).
37 *
38 * The coefficient controller will deliver data to us one iMCU row at a time;
39 * each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
40 * exactly min_DCT_scaled_size row groups. (This amount of data corresponds
41 * to one row of MCUs when the image is fully interleaved.) Note that the
42 * number of sample rows varies across components, but the number of row
43 * groups does not. Some garbage sample rows may be included in the last iMCU
44 * row at the bottom of the image.
45 *
46 * Depending on the vertical scaling algorithm used, the upsampler may need
47 * access to the sample row(s) above and below its current input row group.
48 * The upsampler is required to set need_context_rows TRUE at global selection
49 * time if so. When need_context_rows is FALSE, this controller can simply
50 * obtain one iMCU row at a time from the coefficient controller and dole it
51 * out as row groups to the postprocessor.
52 *
53 * When need_context_rows is TRUE, this controller guarantees that the buffer
54 * passed to postprocessing contains at least one row group's worth of samples
55 * above and below the row group(s) being processed. Note that the context
56 * rows "above" the first passed row group appear at negative row offsets in
57 * the passed buffer. At the top and bottom of the image, the required
58 * context rows are manufactured by duplicating the first or last real sample
59 * row; this avoids having special cases in the upsampling inner loops.
60 *
61 * The amount of context is fixed at one row group just because that's a
62 * convenient number for this controller to work with. The existing
63 * upsamplers really only need one sample row of context. An upsampler
64 * supporting arbitrary output rescaling might wish for more than one row
65 * group of context when shrinking the image; tough, we don't handle that.
66 * (This is justified by the assumption that downsizing will be handled mostly
67 * by adjusting the DCT_scaled_size values, so that the actual scale factor at
68 * the upsample step needn't be much less than one.)
69 *
70 * To provide the desired context, we have to retain the last two row groups
71 * of one iMCU row while reading in the next iMCU row. (The last row group
72 * can't be processed until we have another row group for its below-context,
73 * and so we have to save the next-to-last group too for its above-context.)
74 * We could do this most simply by copying data around in our buffer, but
75 * that'd be very slow. We can avoid copying any data by creating a rather
76 * strange pointer structure. Here's how it works. We allocate a workspace
77 * consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
78 * of row groups per iMCU row). We create two sets of redundant pointers to
79 * the workspace. Labeling the physical row groups 0 to M+1, the synthesized
80 * pointer lists look like this:
81 * M+1 M-1
82 * master pointer --> 0 master pointer --> 0
83 * 1 1
84 * ... ...
85 * M-3 M-3
86 * M-2 M
87 * M-1 M+1
88 * M M-2
89 * M+1 M-1
90 * 0 0
91 * We read alternate iMCU rows using each master pointer; thus the last two
92 * row groups of the previous iMCU row remain un-overwritten in the workspace.
93 * The pointer lists are set up so that the required context rows appear to
94 * be adjacent to the proper places when we pass the pointer lists to the
95 * upsampler.
96 *
97 * The above pictures describe the normal state of the pointer lists.
98 * At top and bottom of the image, we diddle the pointer lists to duplicate
99 * the first or last sample row as necessary (this is cheaper than copying
100 * sample rows around).
101 *
102 * This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
103 * situation each iMCU row provides only one row group so the buffering logic
104 * must be different (eg, we must read two iMCU rows before we can emit the
105 * first row group). For now, we simply do not support providing context
106 * rows when min_DCT_scaled_size is 1. That combination seems unlikely to
107 * be worth providing --- if someone wants a 1/8th-size preview, they probably
108 * want it quick and dirty, so a context-free upsampler is sufficient.
109 */
110
111
112 /* Private buffer controller object */
113
114 typedef struct {
115 struct jpeg_d_main_controller pub; /* public fields */
116
117 /* Pointer to allocated workspace (M or M+2 row groups). */
118 JSAMPARRAY buffer[MAX_COMPONENTS];
119
120 boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
121 JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
122
123 /* Remaining fields are only used in the context case. */
124
125 /* These are the master pointers to the funny-order pointer lists. */
126 JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
127
128 int whichptr; /* indicates which pointer set is now in use */
129 int context_state; /* process_data state machine status */
130 JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
131 JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
132 } my_main_controller;
133
134 typedef my_main_controller * my_main_ptr;
135
136 /* context_state values: */
137 #define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
138 #define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
139 #define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
140
141
142 /* Forward declarations */
143 METHODDEF(void) process_data_simple_main
144 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
145 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
146 METHODDEF(void) process_data_context_main
147 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
148 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
149 #ifdef QUANT_2PASS_SUPPORTED
150 METHODDEF(void) process_data_crank_post
151 JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
152 JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
153 #endif
154
155
156 LOCAL(void)
157 alloc_funny_pointers (j_decompress_ptr cinfo)
158 /* Allocate space for the funny pointer lists.
159 * This is done only once, not once per pass.
160 */
161 {
162 my_main_ptr main = (my_main_ptr) cinfo->main;
163 int ci, rgroup;
164 int M = cinfo->min_DCT_scaled_size;
165 jpeg_component_info *compptr;
166 JSAMPARRAY xbuf;
167
168 /* Get top-level space for component array pointers.
169 * We alloc both arrays with one call to save a few cycles.
170 */
171 main->xbuffer[0] = (JSAMPIMAGE)
172 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
173 cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
174 main->xbuffer[1] = main->xbuffer[0] + cinfo->num_components;
175
176 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
177 ci++, compptr++) {
178 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
179 cinfo->min_DCT_scaled_size; /* height of a row group of component */
180 /* Get space for pointer lists --- M+4 row groups in each list.
181 * We alloc both pointer lists with one call to save a few cycles.
182 */
183 xbuf = (JSAMPARRAY)
184 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
185 2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
186 xbuf += rgroup; /* want one row group at negative offsets */
187 main->xbuffer[0][ci] = xbuf;
188 xbuf += rgroup * (M + 4);
189 main->xbuffer[1][ci] = xbuf;
190 }
191 }
192
193
194 LOCAL(void)
195 make_funny_pointers (j_decompress_ptr cinfo)
196 /* Create the funny pointer lists discussed in the comments above.
197 * The actual workspace is already allocated (in main->buffer),
198 * and the space for the pointer lists is allocated too.
199 * This routine just fills in the curiously ordered lists.
200 * This will be repeated at the beginning of each pass.
201 */
202 {
203 my_main_ptr main = (my_main_ptr) cinfo->main;
204 int ci, i, rgroup;
205 int M = cinfo->min_DCT_scaled_size;
206 jpeg_component_info *compptr;
207 JSAMPARRAY buf, xbuf0, xbuf1;
208
209 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
210 ci++, compptr++) {
211 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
212 cinfo->min_DCT_scaled_size; /* height of a row group of component */
213 xbuf0 = main->xbuffer[0][ci];
214 xbuf1 = main->xbuffer[1][ci];
215 /* First copy the workspace pointers as-is */
216 buf = main->buffer[ci];
217 for (i = 0; i < rgroup * (M + 2); i++) {
218 xbuf0[i] = xbuf1[i] = buf[i];
219 }
220 /* In the second list, put the last four row groups in swapped order */
221 for (i = 0; i < rgroup * 2; i++) {
222 xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
223 xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
224 }
225 /* The wraparound pointers at top and bottom will be filled later
226 * (see set_wraparound_pointers, below). Initially we want the "above"
227 * pointers to duplicate the first actual data line. This only needs
228 * to happen in xbuffer[0].
229 */
230 for (i = 0; i < rgroup; i++) {
231 xbuf0[i - rgroup] = xbuf0[0];
232 }
233 }
234 }
235
236
237 LOCAL(void)
238 set_wraparound_pointers (j_decompress_ptr cinfo)
239 /* Set up the "wraparound" pointers at top and bottom of the pointer lists.
240 * This changes the pointer list state from top-of-image to the normal state.
241 */
242 {
243 my_main_ptr main = (my_main_ptr) cinfo->main;
244 int ci, i, rgroup;
245 int M = cinfo->min_DCT_scaled_size;
246 jpeg_component_info *compptr;
247 JSAMPARRAY xbuf0, xbuf1;
248
249 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
250 ci++, compptr++) {
251 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
252 cinfo->min_DCT_scaled_size; /* height of a row group of component */
253 xbuf0 = main->xbuffer[0][ci];
254 xbuf1 = main->xbuffer[1][ci];
255 for (i = 0; i < rgroup; i++) {
256 xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
257 xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
258 xbuf0[rgroup*(M+2) + i] = xbuf0[i];
259 xbuf1[rgroup*(M+2) + i] = xbuf1[i];
260 }
261 }
262 }
263
264
265 LOCAL(void)
266 set_bottom_pointers (j_decompress_ptr cinfo)
267 /* Change the pointer lists to duplicate the last sample row at the bottom
268 * of the image. whichptr indicates which xbuffer holds the final iMCU row.
269 * Also sets rowgroups_avail to indicate number of nondummy row groups in row.
270 */
271 {
272 my_main_ptr main = (my_main_ptr) cinfo->main;
273 int ci, i, rgroup, iMCUheight, rows_left;
274 jpeg_component_info *compptr;
275 JSAMPARRAY xbuf;
276
277 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
278 ci++, compptr++) {
279 /* Count sample rows in one iMCU row and in one row group */
280 iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
281 rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
282 /* Count nondummy sample rows remaining for this component */
283 rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
284 if (rows_left == 0) rows_left = iMCUheight;
285 /* Count nondummy row groups. Should get same answer for each component,
286 * so we need only do it once.
287 */
288 if (ci == 0) {
289 main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
290 }
291 /* Duplicate the last real sample row rgroup*2 times; this pads out the
292 * last partial rowgroup and ensures at least one full rowgroup of context.
293 */
294 xbuf = main->xbuffer[main->whichptr][ci];
295 for (i = 0; i < rgroup * 2; i++) {
296 xbuf[rows_left + i] = xbuf[rows_left-1];
297 }
298 }
299 }
300
301
302 /*
303 * Initialize for a processing pass.
304 */
305
306 METHODDEF(void)
307 start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
308 {
309 my_main_ptr main = (my_main_ptr) cinfo->main;
310
311 switch (pass_mode) {
312 case JBUF_PASS_THRU:
313 if (cinfo->upsample->need_context_rows) {
314 main->pub.process_data = process_data_context_main;
315 make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
316 main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
317 main->context_state = CTX_PREPARE_FOR_IMCU;
318 main->iMCU_row_ctr = 0;
319 } else {
320 /* Simple case with no context needed */
321 main->pub.process_data = process_data_simple_main;
322 }
323 main->buffer_full = FALSE; /* Mark buffer empty */
324 main->rowgroup_ctr = 0;
325 break;
326 #ifdef QUANT_2PASS_SUPPORTED
327 case JBUF_CRANK_DEST:
328 /* For last pass of 2-pass quantization, just crank the postprocessor */
329 main->pub.process_data = process_data_crank_post;
330 break;
331 #endif
332 default:
333 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
334 break;
335 }
336 }
337
338
339 /*
340 * Process some data.
341 * This handles the simple case where no context is required.
342 */
343
344 METHODDEF(void)
345 process_data_simple_main (j_decompress_ptr cinfo,
346 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
347 JDIMENSION out_rows_avail)
348 {
349 my_main_ptr main = (my_main_ptr) cinfo->main;
350 JDIMENSION rowgroups_avail;
351
352 /* Read input data if we haven't filled the main buffer yet */
353 if (! main->buffer_full) {
354 if (! (*cinfo->coef->decompress_data) (cinfo, main->buffer))
355 return; /* suspension forced, can do nothing more */
356 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
357 }
358
359 /* There are always min_DCT_scaled_size row groups in an iMCU row. */
360 rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
361 /* Note: at the bottom of the image, we may pass extra garbage row groups
362 * to the postprocessor. The postprocessor has to check for bottom
363 * of image anyway (at row resolution), so no point in us doing it too.
364 */
365
366 /* Feed the postprocessor */
367 (*cinfo->post->post_process_data) (cinfo, main->buffer,
368 &main->rowgroup_ctr, rowgroups_avail,
369 output_buf, out_row_ctr, out_rows_avail);
370
371 /* Has postprocessor consumed all the data yet? If so, mark buffer empty */
372 if (main->rowgroup_ctr >= rowgroups_avail) {
373 main->buffer_full = FALSE;
374 main->rowgroup_ctr = 0;
375 }
376 }
377
378
379 /*
380 * Process some data.
381 * This handles the case where context rows must be provided.
382 */
383
384 METHODDEF(void)
385 process_data_context_main (j_decompress_ptr cinfo,
386 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
387 JDIMENSION out_rows_avail)
388 {
389 my_main_ptr main = (my_main_ptr) cinfo->main;
390
391 /* Read input data if we haven't filled the main buffer yet */
392 if (! main->buffer_full) {
393 if (! (*cinfo->coef->decompress_data) (cinfo,
394 main->xbuffer[main->whichptr]))
395 return; /* suspension forced, can do nothing more */
396 main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
397 main->iMCU_row_ctr++; /* count rows received */
398 }
399
400 /* Postprocessor typically will not swallow all the input data it is handed
401 * in one call (due to filling the output buffer first). Must be prepared
402 * to exit and restart. This switch lets us keep track of how far we got.
403 * Note that each case falls through to the next on successful completion.
404 */
405 switch (main->context_state) {
406 case CTX_POSTPONED_ROW:
407 /* Call postprocessor using previously set pointers for postponed row */
408 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
409 &main->rowgroup_ctr, main->rowgroups_avail,
410 output_buf, out_row_ctr, out_rows_avail);
411 if (main->rowgroup_ctr < main->rowgroups_avail)
412 return; /* Need to suspend */
413 main->context_state = CTX_PREPARE_FOR_IMCU;
414 if (*out_row_ctr >= out_rows_avail)
415 return; /* Postprocessor exactly filled output buf */
416 /*FALLTHROUGH*/
417 case CTX_PREPARE_FOR_IMCU:
418 /* Prepare to process first M-1 row groups of this iMCU row */
419 main->rowgroup_ctr = 0;
420 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1);
421 /* Check for bottom of image: if so, tweak pointers to "duplicate"
422 * the last sample row, and adjust rowgroups_avail to ignore padding rows.
423 */
424 if (main->iMCU_row_ctr == cinfo->total_iMCU_rows)
425 set_bottom_pointers(cinfo);
426 main->context_state = CTX_PROCESS_IMCU;
427 /*FALLTHROUGH*/
428 case CTX_PROCESS_IMCU:
429 /* Call postprocessor using previously set pointers */
430 (*cinfo->post->post_process_data) (cinfo, main->xbuffer[main->whichptr],
431 &main->rowgroup_ctr, main->rowgroups_avail,
432 output_buf, out_row_ctr, out_rows_avail);
433 if (main->rowgroup_ctr < main->rowgroups_avail)
434 return; /* Need to suspend */
435 /* After the first iMCU, change wraparound pointers to normal state */
436 if (main->iMCU_row_ctr == 1)
437 set_wraparound_pointers(cinfo);
438 /* Prepare to load new iMCU row using other xbuffer list */
439 main->whichptr ^= 1; /* 0=>1 or 1=>0 */
440 main->buffer_full = FALSE;
441 /* Still need to process last row group of this iMCU row, */
442 /* which is saved at index M+1 of the other xbuffer */
443 main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
444 main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
445 main->context_state = CTX_POSTPONED_ROW;
446 }
447 }
448
449
450 /*
451 * Process some data.
452 * Final pass of two-pass quantization: just call the postprocessor.
453 * Source data will be the postprocessor controller's internal buffer.
454 */
455
456 #ifdef QUANT_2PASS_SUPPORTED
457
458 METHODDEF(void)
459 process_data_crank_post (j_decompress_ptr cinfo,
460 JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
461 JDIMENSION out_rows_avail)
462 {
463 (*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
464 (JDIMENSION *) NULL, (JDIMENSION) 0,
465 output_buf, out_row_ctr, out_rows_avail);
466 }
467
468 #endif /* QUANT_2PASS_SUPPORTED */
469
470
471 /*
472 * Initialize main buffer controller.
473 */
474
475 GLOBAL(void)
476 jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
477 {
478 my_main_ptr main;
479 int ci, rgroup, ngroups;
480 jpeg_component_info *compptr;
481
482 main = (my_main_ptr)
483 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
484 SIZEOF(my_main_controller));
485 cinfo->main = (struct jpeg_d_main_controller *) main;
486 main->pub.start_pass = start_pass_main;
487
488 if (need_full_buffer) /* shouldn't happen */
489 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
490
491 /* Allocate the workspace.
492 * ngroups is the number of row groups we need.
493 */
494 if (cinfo->upsample->need_context_rows) {
495 if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */
496 ERREXIT(cinfo, JERR_NOTIMPL);
497 alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
498 ngroups = cinfo->min_DCT_scaled_size + 2;
499 } else {
500 ngroups = cinfo->min_DCT_scaled_size;
501 }
502
503 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
504 ci++, compptr++) {
505 rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
506 cinfo->min_DCT_scaled_size; /* height of a row group of component */
507 main->buffer[ci] = (*cinfo->mem->alloc_sarray)
508 ((j_common_ptr) cinfo, JPOOL_IMAGE,
509 compptr->width_in_blocks * compptr->DCT_scaled_size,
510 (JDIMENSION) (rgroup * ngroups));
511 }
512 }